Turbocharged engines include compressors that may supply compressed air to the engine to increase engine power. The compressors may experience surge or flow oscillations when a pressure ratio across the compressor is high and flow through the compressor is low. Compressor surge may be graphically depicted via a compressor surge line. The compressor surge line is a line that indicates when a compressor enters surge, and the line may be expressed as a function of compressor pressure ratio and compressor flow. One way to mitigate compressor surge is to allow air to flow from the compressor's outlet to the compressor's inlet via a compressor recirculation valve. By allowing flow from the compressor's outlet to the compressor's inlet, flow through the compressor is increased, thereby allowing the compressor to avoid crossing the surge line and entering a surge condition. However, if the compressor recirculation valve opens farther than desired, such that the flow through the compressor bypass increases more than is desired, vehicle performance may degrade more than is desired.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: providing a first compressor surge line and a second compressor surge line; blending the first compressor surge line and the second compressor surge line into a third compressor surge line; and operating the recirculation valve in response to the third compressor surge line.
By adjusting a compressor recirculation valve position in response to a compressor surge line that is based on a base compressor surge line and a soft compressor surge line, it may be possible to provide the technical result of reducing the possibility of compressor surge while providing acceptable engine performance. For example, a base compressor surge line may be a surge line that if crossed during compressor operation causes compressor flow oscillations that are greater than a threshold. The soft compressor surge line may be a surge line that if crossed during compressor operation causes audible noise that may be undesirable and low amplitude compressor flow rate changes. The base compressor surge line and the soft compressor surge line may be the basis for a surge line that varies based on vehicle performance criteria. If lower vehicle performance is deemed acceptable during present operating conditions, the basis for controlling the compressor is a surge line that is closer to the soft compressor surge line. If higher vehicle performance is desired during present operating conditions, the basis for controlling the compressor is a surge line that is closer to the base compressor surge line.
The present description may provide several advantages. In particular, the approach may provide for acceptable vehicle performance and compressor surge control. Further, the approach may provide vehicle performance that is based on select operating conditions. Additionally, the approach may be applied to a variety of differently configured turbocharged engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.